Microphone



Jan, 7, 1958- l. HELLER MICROPHONE Filed Ju1y 2l.',-.19 55 md H w m mdWmH .T M A nw /M United States Patent MICROPHONE Isaac Heller, Maplewood,N. 1., assignor to Robin Hood (30., Newark, N. L, a corporation of NewJersey Application July 21, 1955, Serial No. 523,538

9 Claims. (Cl. 179-122) This invention relates to microphones and moreparticularly to a new and useful improvement in a carbon granule typemicrophone. Y

One object of the present invention is to provide a novel and improvedconstruction and combination of a diaphragm, a one piece housing ofelectrical insulating material and a combined electrode and containerfor granulated carbon whereby carbon granules can be inserted into andremoved from the microphone from the rear thereof and said container andelectrode can be easily and quickly removed from the housing withoutdisturbing the diaphragm.

Another object of the invention is to provide in a microphone of thischaracter, which includes a sheet silk closure for the chamber thatcontains the granulated carbon, novel and improved means for easily andquickly securing the sheet silk closure in the housing.

It is another object of the invention to provide in such a microphone, anovel and improved vibratile electrode and simple and inexpensive meansfor securing together said vibratile electrode, said silk sheet and saiddiaphragm.

Another object is to provide a microphone that shall comprise aone-piece housing of electrical insulating material, and a stationaryelectrode that shall include a separate cup of insulating materialinserted into the casing and having a cup-shaped lining of metallic foilpossessing a highly conductive electroplated inner surface, separablyinserted into the plastic cup to hold the carbon granules.

A further object is to provide such a microphones which shall be simplein construction, extremely sensitive, faithful in reproducing speechsounds throughout a wide range of angular positions which the microphonemay assume during operation, and which can be manufactured and sold atlow cost.

For a further comprehension of the invention and of the objects andadvantages thereof, reference will be had to the following descriptionand accompanying drawings and to the appended claims in which thevarious novel features of the invention are more particularly set forth.

In the accompanying drawings forming a material part of this disclosure:

Figure 1 is a side elevational view of a microphone embodying myinvention.

Figure 2 is a bottom plan view thereof.

Figure 3 is a top plan view thereof, parts being broken away.

Figure 4 is a vertical sectional view of the microphone taken throughthe center thereof.

Figure 5 is a disassembled view of the fixed electrode and associatedadjusting screw.

Figure 6 is a fragmentary sectional view similar to Figure 4 showing amodification of the stationary electrode, with portions of the diaphragmand of the casing omitted.

Figure 7 is a top plan view of the parts illustrated in Figure 6 withportions broken away and other portions omitted.

Referring in detail to the drawings, a microphone made in accordancewith the invention is shown in Figure 1 and comprises a bowl-shapedsupporting frame 1 formed of suitable insulating material such assynthetic plastic electrical insulating material. The frame is formedpreferably integrally with a cylindrical tubular hub portion 2, open atboth ends and protruding below the bottom of the bowl body, constitutingan annular flange 3. The flaring top end of the frame is formed with aninner shoulder 4 constituting a supporting surface.

A main vibrating diaphragm 5 for receiving the sound vibrations isseated at its periphery on the shoulder tand is clamped in place by aclamping ring 6. The diaphragm 5 may be of a lightweight metal, such asaluminum or thin Duralumin, and is corrugated as indicated at 7.

A stationary or fixed electrode which may be of brass is fitted in thetubular hub portion 2 of the frame and comprises a solid cylindricalmember 8, with its inner end flush with the inner edge of the hubportion and with its outer end flush with the outer edge of the flange3. The inner end of the electrode is dished out in the form of asubstantially frusto-conical-shaped chamber 9, the chamber opening atits larger end through the inner end of the electrode. At its innersmaller end, the chamber communicates with a screw-threaded passage 10leading outwardly of the outer end of the electrode. The inner sur faceof chamber 9 is preferably gold plated to enhance the conductivitythereof.

A closure member in the form of a flexible silk sheet 11 is stretchedover the inner edge of the tubular hub portion 2 and over the inner endof the electrode 8 thereby sealing the chamber 9 in the electrode andserving as an auxiliary diaphragm. The silk closure member has afullness overlying the outer surface of the hub portion 2 of the frame 1and is clamped in position by a flanged ring 12 preferably of plasticmaterial.

A metallic electrode having a generally frusto-com'cal body portion 13having a convexly curved top and a slightly out-turned curved base 14,is disposed in the center of the chamber 9 of the fixed electrode 8. Thefrusto-conical body portion 13 is fixed to the central depressed portion15 of the main diaphragm 5 by means of a rivet 1.6, the rivet extendingthrough aligned openings in the closure member 11 and diaphragm 5. Awasher 17 is interposed between the diaphragm 5 and the outer upset headof the rivet. The outer surface of the frusto-conical body portion 13 ofthe vibratile electrode is preferably gold plated. The silk closuremember 11 is clamped at its center between the main diaphragm 5 and thebase 14 of the vibratile electrode. 7

A quantity of a comminuted resistance-varying mate rial such as carbongranules 18 is inserted through the passage 10 in the fixed electrode 8and is packed in and substantially fills the chamber 9 bounded by thefixed and vibratile electrodes and the silk closure member 11.Vibrations of the main diaphragm 5 are communicated to the comminutedmaterial and the resistance between the electrodes 8 and 13 is therebyvaried. The passage 10 in the bottom of the fixed electrode 8 throughwhich the carbon granules are introduced is closed by an ad justingscrew 19 having a knurled head constituting a finger piece 20. A knurledlock nut 21 is provided on the screw for clampingly connecting aconductor (not shown) to the screw between the electrode 8 and the nut21. By moving the screw, the compactness of the mass of carbon granulesmay be adjusted.

When the microphone is in operation, the current flow takes place overthe following path: from the conductor attached to the screw 19 to saidscrew, then from the high degree of uniform action of the comminutedcarbon granules in varying the current flow in response to diaphragmmovements, in whatever position-the microphone may be placed.

In addition to the formation of the chamber serving to properly maintainthe comminuted carbongranules in l uniform arrangement and compactness,the frustoconical formation of the electrode 13 provides anadvantageousand effective movable contact for accurately conveying to.

the compressible carbon mass the varying-pressure elfects derived fromdiaphragm movements.

It will be seen that the brass'cylinder constituting the fixed electrode8 may be readily withdrawnfromthe tubular hub portion 2 of the frameby-manuallypulling on the screw 19, the finger piece serving as a handlefor this purpose, leaving the remaining elements of the microphoneundisturbed, and in position for ready disassembly if desired. The outersurface of the cylinder-8 may be roughened as indicated at 22 to.hold,itin place.

A modification of the stationary electrode is. shown in Figures 6 and 7where theelectrode comprises a'cup 23 of electro-insulating materialthat is nicely:fitted into the tubular hub portion 24 of the, housing orframe 25. Preferably the cup and the inner wall of the hub portion 24have the respective abuttingshoulders 26and27 .to

limit the insertion'of thecupintoithe.hubiportioni The inner end of thecuphas a frusto-conical shaped chamber 28, the open end of whichisflared at 29, andseated in the chamber 28 is a lining 30. of.metallicfoil that preferably has an electroplated highly conductive i concaveinner surface to contact withthecarbon granules. (notshown) in the samemanner in whichithe granules 18 contact the wall of the chamber 9 in theconstruction shown iii-Figure 4. The foil lining 30.:mayinitiallyicomprise ,a flat-cir-.

cular sheet or disk of foil; whichzmayrbe .laid,over the open end of thechamber 28. and, then pressed into'thev chamber to bring the foil intoclose contact with the wallsv of the chamber, the,foil'beingtfoldedonpleated; to per,- mit the sheet to be deformedjntothe concave cup-like,

shape. The auxiliary silk diaphragm 111 is stretched over the edge ofthe hub portion124 and securedby the, flanged ring 12 in the samemanenthattheauxiliary diaphragm 11 is secured by the flange; ring 12 Atthe bottom of theschamber r 28. and ;coaxial;,there-. with is an opening31 thatopensthroughthcnend of; the A plastic cup, and into this openingis,sc rewed;a self+tapping screw 32 which hasa reduced inner end 33 thatnormally is snugly disposedin an opening punched: in the. bottom of thelining so as to provide an electrical contact between the screw and thelining, and to permitthe screw.

to be used in the same mannerjas the screw 19 for-connecting thestationary electrode in a circuit.

The plastic cup 23 maybe tightlyfrictionally, fitted in, the hub portion24 but preferably is secured byadhesive, i

and the cup-shaped lining. 30, is. clampedbetweenthe screw 3?. and theauxiliary diaphragm II. The carbon granules may be inserted; throughthe;opening- Bland lightlyclamped between the auxiliary diaphragm .ll'.and.

the inner end 33 of thescrew 32.,

While I have illustrated. and described v the ,preferred. embodiment ofmy invention, it willtbetunderstood that changes in detailsofconstructioni-might-be made .within.

the principle and scope of theinventiou and ,I desire therefore to belimited ,onlyby.theistateof-the-prior, art and the appended claims.

Having thusdescribed the invention, what. I claimas- 4- new and desireto secure by United States Letters Patent is:

l. A microphone comprising a one piece frame open at its front and rearends, a diaphragm secured upon the front end of the frame, a combinedstationary electrode and container for granulate/J carbon removablyfitted into the rear end of said frame and having a concave inner endportion, a non-conductive flexible auxiliary diaphragm secured on saidframe in overlying relation to said concave inner end and providingachamber, granulated carbon in said chamber; a-vibratile electrodedisposed in said chamber in contact with said granulated carbon andcomprising a hollow generally frustowconical body having a convex curvedend extending into the concave end of said combined stationary electrodeand container, and a fastening member passing through and rigidlyconnecting said vibratile electrode, said auxiliary diaphragm and saiddiaphragm.

2. A microphone comprising an insulating bowlshaped frame with a tubularhub portion, a main metallic diaphragm clamped to the outer edge'of saidframe, an electrically conductive cylindrical member in said hub portionconstituting a fixed electrode, said cylindrical member having adished-out chamber at its inner end. an auxiliary non-conductiveflexible diaphragm sealing the inner end of the chamber, means ofconnection between said auxiliary diaphragm and said main diaphragm, afrusto-conical shaped electrode in said chamber connected toboth of saiddiaphragms, and carbon granules in the chamber between said electrodes.

3. A microphone comprising an insulating bowlshaped frame with a tubularhub portion open at both ends, a main metallic diaphragm clamped to theouter edgeof said frame, an electrically conductive cylindrical memberin said hub portion constituting a fixed electrode. said cylindricalmember having a dished-out chamber at its inner end andhavinga centralpassage at its outer end communicating withsaid chamber, carbon granulesin the chamber between said electrodes, an auxiliary nonconductiveflexible diaphragm of silk sealing the inner end of the chamber, meansof connection between said auxiliary diaphragm and said main diaphragm,a frustoconical shaped electrode insaid chamber connected to both ofsaid diaphragms, and means for plugging the pas-- sage leading to saidchamber.

4. A microphone comprising an insulating bowlshaped frame with a tubularhub portion open at both ends,- a main metallic diaphragm clamped to theouter edge of said frame, an electrically conductive cylindrical memberin said hub portion constituting a fixed electrode, said cylindricalmember having a dished-out chamber at its inner end and having a centralpassage at its outer end communicating with said chamber, carbongranules in the chamber between said electrodes, an auxiliarynonconductive flexible diaphragm of silk sealing the inner end of thechamber, means of connection between said auxiliary diaphragm and saidmain diaphragm, a frustoconical shaped electrode in said chamberconnected to both of said diaphragms, and a screw plugging said passage,said screw having a protruding head for clamping a conductor to thefixed electrode.

5. A microphone comprising an, insulating bowlshaped frame with atubular hub portion open at both ends, a main metallic diaphragm clampedto the outer edge. of said frame, an electrically conductive cylindricalmember in said hub portionconstituting a fixed electrode, saidcylindrical member having a dished-out chamber at its inner end,.anauxiliary non-conductive flexiblediaphragm stretched across the innerend of said chamber and over the inner endedge of said hub portion.means of-connection between said auxiliary diaphragm and said maindiaphragm, a frusto-conical shaped electrode in said chamber connectedto both of said diaphragms, carbongranules in the chamber betweensaidelectrodes, and a flanged ring clamped over said auxil-' iary diaphragmfor securing same in place on the fixed electrode and hub portion.

6. A microphone comprising an insulating bowl-shaped frame with atubular hub portion open at both ends, a main metallic diaphragm clampedto the outer top end edge of said frame, an electrically conductivecylindrical member removably mounted in said hub portion through theopen bottom end thereof, said cylindrical member constituting a fixedelectrode, said cylindrical member having a dished-out chamber at itsinner end, an auxiliary non-conductive flexible diaphragm sealing theinner end of the chamber, means of connection between said auxiliarydiaphragm and said main diaphragm, a frustoconical shaped electrode insaid chamber connected to both of said diaphragms, carbon granules inthe chamber between said electrodes, 3. portion of the outer surface ofsaid cylindrical member being roughened, said cylindrical member havinga bottom passage leading to said chamber, and a screw plugging saidpassage, said screw having a protruding head serving as a finger piecefor ready withdrawal of the cylindrical member.

7. A microphone as defined in claim 1 wherein the combined stationaryelectrode and container comprises a cup of insulating material and aseparate lining of metallic foil in said cup,

8. A microphone as defined in claim 7 wherein said cup has a coaxialopening and a screw threaded into said opening with its inner end indirect electrical contact with said lining.

9. A microphone comprising a one piece frame open at its front and rearends, a diaphragm secured upon the front end of the frame, a combinedstationary electrode and container for granulated carbon removablyfitted into the rear end of said frame and having a concave inner endportion, a non-conductive flexible auxiliary diaphragm secured on saidframe in overlying relation to said concave inner end and providing achamber, granulated carbon in said chamber, a vibratile electrodedisposed in said chamber in contact with said granulated carbon at theside of said auxiliary diaphragm opposite said diaphragm, and afastening member connected to the center of said vibratile electrode andpassing through said diaphragm and said auxiliary diaphragm and rigidlyconnecting together said vibratile electrode, said auxiliary diaphragmand said diaphragm.

References Cited in the file of this patent UNITED STATES PATENTS2,042,822 Bennett et al. June 2, 1936 FOREIGN PATENTS 550,362 GreatBritain Jan. 5, 1943 611,414 Great Britain Oct. 29, 1948

